PROJECT SUMMARY ?-lactams comprise more than half of all antibacterials used globally for treatment of bacterial infections. Carbapenems, a sub-class of ?-lactams, are one of the most potent antibacterials available and often used as the last resort to treat infections that are not readily treatable with other antibacterials. Among ?-lactams, only carbapenems have therapeutically valuable activity against Mycobacterium tuberculosis (the pathogen that causes tuberculosis) and Mycobacterium abscessus (an opportunistic pathogen that is highly resistant to most antibiotics and is emerging as a major cause of chronic infections in cystic fibrosis patients). Older carbapenems such as meropenem and imipenem are used for treatment of infections with strains (of these mycobacteria) that are resistant to commonly used drugs. M. abscessus that is resistant to meropenem and imipenem, two powerful carbapenem drugs that are currently in clinical use, are routinely seen in US hospitals. Enhanced potencies of newer carbapenems such as doripenem and biapenem against these mycobacteria has resulted in an increasing use of these carbapenems for treatment of drug resistant forms of tuberculosis and Mycobacterium abscessus infections. It may only be a matter of time before strains of mycobacteria that are resistant to newer carbapenems emerge and thereby reduce the arsenal of antibiotics available to treat these infections. As a proactive measure, we propose to identify genetic mutations that confer mycobacteria resistance to doripenem and biapenem and determine the molecular mechanism of such resistance. Both clinically isolated carabpenem resistant strains and those generated in a controlled setting in the lab will be used to unveil genetic mutations and mechanism that confers resistance to carbapenems. Data from this study will facilitate development of new regimens that are urgently needed for treatment of drug resistant forms of Mycobacterium tuberculosis and Mycobacterium abscessus infections.